Laser beam optical scanning over a surface has been used to melt or sinter materials for additive manufacturing and for purposes such as hardfacing, corrosion overlay, refurbishment or cladding. It is often valuable to provide a uniform power (and/or energy or heat) distribution to the surface to ensure minimal and consistent melting of the substrate, and thus low and uniform dilution. Low dilution is important for application of hardfacing, corrosion overlay or for refurbishment cladding—especially with materials that are difficult to weld because they are prone to cracking. Uniform power distribution is also important for uniform transformation hardening of surfaces. For cladding of broad areas, buildups in grooves, and hardening of complex surfaces such as gear teeth, customized optics such as mirrors rocked by specifically contoured cams were developed by the present inventor in the late 1980's. Such motor driven laser mirrors have been superseded by advanced galvanometer driven optics capable of moving the beam in three dimensions.
In conjunction with robotics, such optics are used for spot welding in automotive parts manufacture. Rastered laser cladding has also been performed with such optics. There are two common modes of rastering with such optics—“wobble” and “normal”. In wobble rastering, the beam follows a path similar to the projection of a helical spring as viewed from the side. The beam spends more time at the ends of the scan lines, resulting in a power distribution to the substrate that applies more power at such locations and less at the center. This can result in over-melting at the sides producing inconsistent surface properties.
Normal rastering resolves the issue of over-melting associated with wobble rastering. With normal rastering, scanning is performed from left to right with periodic incrementing forward. The forward incrementing is nearly instantaneous compared to the left to right motion, so power distribution is nearly uniform over the area being exposed.
While normal scanning solves the issue of over-melting at both sides of the scan, an additional problem persists. That is, normal scanning provides uniform power for straight linear paths, but where the path curves or, for example, turns a corner, forward incrementing at the outer edge of the corner must be relatively large compared to forward incrementing at the inner edge of the corner in order to cover the larger circumferential distance at the larger radius. This results in a power density that is not uniform over the area being processed.